The invention relates to a method and a system preparing samples for gas chromatography.
In order to prepare samples for gas chromatography, it is known to connect a liquid chromatograph (LC) upstream of the gas chromatograph (GC). For this purpose, in on-line operation, a valve circuit with fixed bypass injector is used. Immediately after passing an LC detector, the sample material is removed from the LC and conveyed via a transfer line to a complicated valve device which is connected in such a way that the sample material contained in the bypass injector is flushed directly into a gas-chromatography capillary column using a carrier gas. However, such columns have only a limited sample capacity, so that this operation is possible only by employing complicated coupled-column technique comprising up to three series-connected capillary columns, firstly a gas-chromatographically inactive column for holding the sample material, then a precolumn for blending out the solvent, and finally a main column for the chromatographic separation. A so-called early-vapor exit is situated between the latter two columns. In this case, the bypass injector can only be changed by means of costly modification of the device. There are not possibilities for variation, and only the start of feed to the inactive column, and hence the selection of the starting point of a chromatographic region of interest, can be influenced.
In off-line operation, the sample material, downstream of the LC, is in sample bottles of a fraction collector, in order then to be analyzed further in a conventional manner.